1. Field of the Invention
The present invention relates to a hydrogen absorbing alloy powder comprising a hydrogen absorbing alloy and used, for example, in nickel-metal hydride batteries, and a nickel-metal hydride battery using the same.
2. Description of the Related Art
Since electrodes using hydrogen absorbing alloy powder have a theoretical capacitance density larger than that of cadmium electrode and do not suffer from deformation or cause formation of dendrites such as in zinc electrodes, they have long life and result in no public pollution. In addition, since they show high energy density, they are often used, for example, as a power supply for use in small-sized portable devices as a negative electrode of nickel-metal hydride batteries. The nickel-metal hydride batteries have attracted attention in recent years also as electric sources for engine power such as for electric vehicles or hybrid cars and it has been strongly demanded for the improvement in output characteristics or storage characteristics.
One of the methods includes a treatment of increasing the activity of a hydrogen absorbing alloy powder used as the negative electrode active material of nickel-metal hydride batteries and various proposals have been given.
One of them is disclosed in Jpn. unexamined patent publication No. 2002-256301. For providing an alloy powder for use in an electrode capable of providing alkali batteries excellent in high rate discharging characteristics, self-discharging characteristics, and cycle characteristics, this publication '301 discloses a method of producing an alloy powder for use in an electrode, including a first step of dipping a starting material comprising a hydrogen absorbing alloy containing from 20% to 70% by weight of Ni in an aqueous solution that contains from 30% to 80% by weight of sodium hydroxide at 90° C. or higher, and a second step of water washing the powder applied with the first step.